poj 1284 Primitive Roots

Description
We say that integer x, 0 < x < p, is a primitive root modulo odd prime p if and only if the set { (xi mod p) | 1 <= i <= p-1 } is equal to { 1, …, p-1 }. For example, the consecutive powers of 3 modulo 7 are 3, 2, 6, 4, 5, 1, and thus 3 is a primitive root modulo 7.
Write a program which given any odd prime 3 <= p < 65536 outputs the number of primitive roots modulo p.

Input
Each line of the input contains an odd prime numbers p. Input is terminated by the end-of-file seperator.

Output
For each p, print a single number that gives the number of primitive roots in a single line.

Sample Input

23
31
79

Sample Output

10
8
24

#include<cstdio>
int phi(int v){
    int i,s=v;
    for(i=2;i*i<=v;i++){
        if(v%i==0){
            s-=s/i;
        }
        while(v%i==0) v/=i;
    }
    if(v>1)
        s-=s/v;
    return s;
}
int main(){
    int n;
    while(scanf("%d",&n)==1)
        printf("%d\n",phi(n-1));
    return 0;
}